There are air humidifiers on the market which either operate on the principle of a heated water vessel, with centrifugal disks or by electronic atomizers that disintegrate the water into tiny droplets.
Austrian Patent 391 753 discloses a device for the humidification of air which consists of a vertical pipe socket into the interior of which water droplets fall against upstreaming air down into a collecting container, just as in a sprinkling installation, from where the water is pumped up again and disintegrated into single droplets by a perforated disk. This device is noisy and the droplets hit the water in the container with an audible splash. Some of the moisture already taken up by the upstreaming air is lost again when the air bubbles through the water in the perforated bottom of a water container.
The apparatus described in German Patent Document DE 43 29 209 A1 has a vessel with a built-in trickling installation and splash plates for water through which air is led. The apparatus is in the category of technological air humidifiers, especially for ventilation or air conditioning installations.
Many types of existing types of humidifier are hygrostatically controlled or are equipped with a time control. The first above-mentioned type of humidifier, often referred to as "water kettle", has a low noise level but a high energy demand. The second type, though lower in energy demand, is characterized by irritating noises from the motors for the centrifugal disks or the fans.
A humidifier has been developed, as described in Austrian Patent 373 378 B, which features a water guiding body with a surface over which the water flows, fully covering the surface, which is as large as possible.
The guiding body is situated in a water collecting container from which the water is drawn by a pump and delivered upwards through a central hole in the body.
The intake is adjusted so that the whole surface of the guiding body is covered with water, thus obtaining a rather high rate of evaporation. The water guiding body is designed by an artist and the collecting container, which is also made from stone, complements the overall aesthetic impression. Depending on the adjustment of the intake, the noise to be heard is a soft water murmur or splashing, which is pleasant and calming, for offices as well as for conference, meeting and waiting rooms.
In this connection German Patent Document DE 25 34 524 A1 describes a humidifier which, like a picture, is mounted on a wall and consists of a frame-like housing whose back is shaped as a three-dimensional wall with protruding cascades. The surface of this wall acts as a water guiding body and is thus supplied with water which is collected in the bottom part of the frame and then repumped to the upper portion. This cascade relief humidifies the air passing over the area within the frame. One version shows an integral design of frame and wall, giving the impression of a cascade in the rear of a goggle-box picture. The performance of a humidifier based on natural surface evaporation must be carefully adjusted to the air volume of the room. Large rooms such as cashier areas in banks and hotel lobbies require comparatively large water guiding bodies, and certain areas require intensive air humidifying although there is not enough room for large fountains. Another point to be considered is that large vaporizing units with large surfaces are very heavy and thus often cannot be installed on the upper floors of buildings without appropriate reinforcement of the floor or the ceiling.